Systems and methods for controlling battery current

ABSTRACT

A battery system comprising multiple battery packs. A battery pack of the battery packs includes a battery, voltage sense circuitry, a control circuit, a control switch and current regulation circuitry. The voltage sense circuitry senses a battery voltage of the battery and an input voltage of the battery pack. The control circuit is coupled to the sense circuitry and is operable for adjusting a level of a reference signal based on attribute data associated with the battery pack and a difference between the battery voltage and the input voltage. The control switch is operable for passing a battery current flowing through the battery. The current regulation circuitry is coupled to the control circuit and the control switch, and is operable for controlling the control switch to regulate the battery current according to the reference signal.

REFERENCE TO RELATED APPLICATION

This application claims benefit under 35 U.S.C. § 119(a) to ApplicationNo. GB1703872.0, filed with the United Kingdom Intellectual PropertyOffice on Mar. 10, 2017, hereby incorporated herein by reference in itsentirety.

BACKGROUND

FIG. 1 illustrates a conventional battery management module 100. In thebattery management module 100, if the battery voltage of the battery 102is in a normal operation range, the battery management unit (BMU) 104can turn on the charge switch N_(CHG) to pass a normal charging currentI_(CHG) to charge the battery 102. If the battery voltage is below thenormal operation range, e.g., the battery 102 is over-drained, then theBMU 102 turns on the pre-charge switch P_(CHG) to pass a pre-chargecurrent I_(PCHG), e.g., trickle current, to charge the battery 102. Thepre-charge resistor R_(PCHG) coupled to the pre-charge switch P_(CHG)has relatively high resistance to control the pre-charge currentI_(PCHG) to be relatively small, so as to protect the over-drainedbattery 102.

The battery management module 100 has some shortcomings. For example,the pre-charge current I_(PCHG) can be given by:I_(PCHG)=(V_(PACK+)−V_(BATT))/R_(PCHG), where V_(PACK+) represents avoltage at the input terminal PACK+, and V_(BATT) represents a voltageat the positive terminal of the battery 102. Thus, the pre-chargecurrent I_(PCHG) decreases if the battery voltage V_(BATT) increases,and this slows down the pre-charging process. In addition, thepre-charge resistor R_(PCHG) consumes additional power when thepre-charge current I_(PCHG) flows therethrough. Moreover, the pre-chargeresistor R_(PCHG) and switch P_(CHG) are high-power elements capable ofsustaining a high voltage difference between the input voltage V_(PACK+)and the battery voltage V_(BATT), and therefore they are relativelyexpensive and increase the cost of the battery management module 100.Furthermore, the pre-charge resistor R_(PCHG) and switch P_(CHG)increase the PCB size for the battery management module 100.

A battery management module that addresses the abovementionedshortcomings would be beneficial.

SUMMARY

A battery system comprising multiple battery packs. A battery pack ofthe battery packs includes a battery, voltage sense circuitry, a controlcircuit, a control switch and current regulation circuitry. The voltagesense circuitry senses a battery voltage of the battery and an inputvoltage of the battery pack. The control circuit is coupled to the sensecircuitry and is operable for adjusting a level of a reference signalbased on attribute data associated with the battery pack and adifference between the battery voltage and the input voltage. Thecontrol switch is operable for passing a battery current flowing throughthe battery. The current regulation circuitry is coupled to the controlcircuit and the control switch, and is operable for controlling thecontrol switch to regulate the battery current according to thereference signal.

BRIEF DESCRIPTION OF THE DRAWINGS

Features and advantages of embodiments of the claimed subject matterwill become apparent as the following detailed description proceeds, andupon reference to the drawings, wherein like numerals depict like parts,and in which:

FIG. 1 illustrates a conventional battery management module topology.

FIG. 2A illustrates an example of a battery management module topology,in an embodiment of the present invention.

FIG. 2B illustrates an example of a battery management module topology,in an embodiment of the present invention.

FIG. 3A illustrates an example of a signal waveform of the batterymanagement module in FIG. 2B, in an embodiment of the present invention.

FIG. 3B illustrates an example of a signal waveform of the batterymanagement module in FIG. 2B, in an embodiment of the present invention.

FIG. 4 illustrates an example of a battery management module topology,in an embodiment of the present invention.

FIG. 5 illustrates an example of a battery system topology, in anembodiment of the present invention.

FIG. 6 illustrates a flowchart of examples of operations performed by abattery management module, in an embodiment of the present invention.

FIG. 7 illustrates an example of a battery management module topology,in an embodiment of the present invention.

FIG. 8 illustrates an example of a battery management module topology,in an embodiment of the present invention.

FIG. 9 illustrates an example of a battery management module topology,in an embodiment of the present invention.

FIG. 10 illustrates an example of an expandable battery system, in anembodiment of the present invention.

FIG. 11 illustrates a flowchart of examples of operations performed by abattery management module, in an embodiment of the present invention.

DETAILED DESCRIPTION

Reference will now be made in detail to the embodiments of the presentinvention. While the invention will be described in conjunction withthese embodiments, it will be understood that they are not intended tolimit the invention to these embodiments. On the contrary, the inventionis intended to cover alternatives, modifications and equivalents, whichmay be included within the spirit and scope of the invention as definedby the appended claims.

Furthermore, in the following detailed description of the presentinvention, numerous specific details are set forth in order to provide athorough understanding of the present invention. However, it will berecognized by one of ordinary skill in the art that the presentinvention may be practiced without these specific details. In otherinstances, well known methods, procedures, components, and circuits havenot been described in detail as not to unnecessarily obscure aspects ofthe present invention.

In an embodiment of the present invention, a battery management modulecan control a charge switch to charge a battery according to thebattery's status. For example, the battery management module can fullyturn on the charge switch to operate in a normal charge mode if thebattery voltage is in a normal operation range. The battery managementmodule can also alternately turn on and off the charge switch to operatein a pre-charge mode if the battery voltage is below the normaloperation range. In the pre-charge mode, the battery management modulemay increase a pre-charge current flowing through the charge switch asthe battery voltage increases. As a result, compared with theconventional battery management module 100, the battery managementmodule in an embodiment of the present invention can speed up thepre-charging process. Additionally, the pre-charge resistor R_(PCHG) andswitch P_(CHG) mentioned in FIG. 1 are omitted, and therefore thebattery management module in an embodiment of the present invention canconsume less power, cost less, and has a smaller PCB size compared withthe conventional battery management module 100.

FIG. 2A illustrates a topology of an example of a battery managementmodule 200, in an embodiment of the present invention. The batterymanagement module 200 can be integrated in a battery pack. In anembodiment, the battery management module 200 includes a battery 202(e.g., including a plurality of battery cells), a control switch 220(e.g., a charge switch or a discharge switch), a current sense element(e.g., including a resistor R_(SEN)), and a battery management unit(BMU) 204. In the example of FIG. 2A, the control switch 220, e.g., acharge switch, can pass a battery current I_(CHG), e.g., a pre-chargingcurrent, from a power source (not shown) coupled to the input terminalPACK+ to charge the battery 202. The BMU 204 can receive a first sensesignal V_(SEN), e.g., a voltage signal indicative of the battery currentI_(CHG), from the sense resistor R_(SEN), receive a second sense signal,indicative of a voltage V_(BATT) of the battery 202, and control thecontrol switch 220 according to the sense signals.

More specifically, in an embodiment, the BMU 204 includes comparisoncircuitry 214, current generating circuitry 238, a control circuit 212(e.g., having a control logic residing thereon), a battery-voltage(V_(BATT)) sense circuit 208, and an input-voltage (V_(PACK)) sensecircuit 210. The comparison circuitry 214 can compare the sense signalV_(SEN) with a reference signal 222 to generate a comparison result at,e.g., the signal line 236 and/or the signal line 224. The currentgenerating circuitry 238 can generate a control current I_(CTL),according to the comparison result, to charge or discharge a controlterminal G_(C) of the control switch 220 thereby adjusting the batterycurrent I_(CHG) to have a target average level. By way of example, thecontrol switch 220 includes a field-effect transistor, e.g., ametal-oxide semiconductor field-effect transistor, and the controlterminal G_(C) includes a gate terminal of the field-effect transistor.The control current I_(CTL) can charge the gate terminal G_(C) toincrease the gate voltage V_(G) of the control switch 220 and partiallyturn on the switch 220, thereby increasing the battery current I_(CHG).The control current I_(CTL) can also discharge the gate terminal G_(C)to reduce the gate voltage V_(G) thereby turning off the control switch220 to disable/cutoff the battery current T_(CHG). Thus, an averagelevel of the battery current I_(CHG) can be adjusted by adjusting thecontrol current I_(CTL). The abovementioned comparison result can beprovided to the current generating circuitry 238 to adjust the controlcurrent I_(CTL) such that the battery current I_(CHG) is adjusted tohave a target average level.

Additionally, in an embodiment, the control circuit 212 monitors thebattery current I_(CHG), battery voltage V_(BATT), and input voltageV^(PACK+) via the sense resistor R_(SEN) and sense circuits 208 and 210,and controls the target average level according to the monitoredinformation. By way of example, the current generating circuitry 238 canenable the battery current I_(CHG) to flow through the battery 202 in afirst time interval T_(ON) by charging the control terminal G_(C),disable/cutoff the battery current I_(CHG) in a second time intervalT_(OFF) by discharging the control terminal G_(C), and alternatelyenable and disable the battery current I_(CHG) according to themonitored battery current I_(CHG). The control circuit 212 can increasea ratio of the first time interval to a sum T_(CYC) (e.g.,T_(CYC)=T_(ON)+T_(OFF)) of the first and second time intervals, e.g.,T_(ON)/T_(CYC), thereby increasing the target average level if thebattery voltage V_(BATT) increases or if a difference between thebattery voltage V_(BATT) and the input voltage V_(PACK+) decreases.

Thus, the time for the pre-charge process, e.g., during which thebattery voltage V_(BATT) increases from an over-drained voltage level toa voltage level in a normal operation range of the battery 202 in thebattery management module 200 can be less than that in the conventionalbattery management module 100. Additionally, the pre-charge resistorR_(PCHG) and switch P_(CHG) mentioned in FIG. 1 can be omitted in thebattery management module 200, and therefore the battery managementmodule 200 can consume less power, cost less, and has a smaller PCB sizecompared with the conventional battery management module 100.

In an embodiment, the current generating circuitry 238 includes acurrent source 206, a charge pump 218, and a current regulator 216. Thecurrent source 206 can generate a preset current I_(SRC) to charge thecontrol terminal G_(C). In an embodiment, the current source 206 canhave an arbitrary structure as long as the current source 206 is capableof providing a preset current. For example, the current source 206 mayinclude a current mirror. For another example, the current source 206may include a resistive element (e.g., a resistor) having a presetvoltage applied thereon. For yet another example, the current source 206may include a field-effect transistor having a preset gate-sourcevoltage applied thereon. For yet another example, the current source 206may include an operational transconductance amplifier (OTA) having apreset differential input voltage applied thereon. In an embodiment, thecharge pump 218 can provide a supply voltage, greater than the batteryvoltage V_(BATT), to power the current source 206. Additionally, thecurrent regulator 216 can sink at least a portion of the preset currentI_(SRC) to regulate the control current I_(CTL) according to thecomparison result from the comparison circuitry 214. For example, if thecomparison result indicates that the battery current I_(CHG) is lessthan a reference current level, e.g., indicated by the abovementionedreference signal 222, then the current regulator 216 can be turned offand allow the present current I_(SRC) charge to the control terminalG_(C). If the comparison result indicates that the battery currentI_(CHG) is greater than the reference current level, then the currentregulator 216 generates a sink current I_(BP) to sink at least a portionof the preset current I_(SRC). In an embodiment, the control currentI_(CTL) can charge the control terminal G_(C) to increase the batterycurrent I_(CHG) if the sink current I_(BP) is less than the presetcurrent I_(SRC). The control current I_(CTL) can also discharge thecontrol terminal G_(C) to reduce the battery current I_(CHG) if the sinkcurrent I_(BP) is greater than the preset current I_(SRC). The controlcurrent I_(CTL) can also terminate charging and discharging of thecontrol terminal G_(C) to maintain the battery current I_(CHG) if thesink current I_(BP) remains at the level of the preset current I_(SRC).Thus, the current regulator 216 can regulate the battery current I_(CHG)by controlling the sink current I_(BP).

FIG. 2B illustrates circuit diagrams of examples of the currentregulator 216 and the comparison circuitry 214, in an embodiment of thepresent invention. FIG. 2B is described in combination with FIG. 2A. Asshown in FIG. 2B, the current regulator 216 includes a first switch SW1,a second switch SW2 (e.g., including a metal-oxide-semiconductorfield-effect transistor), a compensation capacitor 230, and a dischargeswitch 234, and the comparison circuitry 214 includes a comparator 214A,an amplifier 214B, e.g., an operational transconductance amplifier(OTA), and reference voltage sources 226 and 228. In an embodiment, thebattery management module 200′ can selectively operate in a first modeor a second mode according to the sense resistance R_(SEN). By way ofexample, if the sense resistance R_(SEN) is too small, e.g., smallerthan specified resistance, then the battery management module 200′operates in the first mode, and the control circuit 212 cooperates withthe comparator 214A and the switch SW1 to adjust the battery currentI_(CHG). If the sense resistance R_(SEN) is not too small, e.g., greaterthan specified resistance, then the battery management module 200′operates in the second mode, and the control circuit 212 cooperates withthe amplifier 214B and the switch SW2 to adjust the battery currentI_(CHG).

More specifically, in the first mode in an embodiment, the voltagesource 226 provides a first reference voltage V_(COC), and thecomparator 214A compares the sense signal V_(SEN) with the referencevoltage V_(COC) to generate a comparison result S_(COC), e.g., a logicsignal. If the sense signal V_(SEN) is greater than the referencevoltage V_(COC), then the comparison result S_(COC) can cause thecontrol circuit 212 to turn on the switch SW1. In an embodiment, whenboth the switches SW1 and SW2 are turned off, the preset current I_(SRC)can charge the control terminal G_(C) to increase the battery currentI_(CHG). When the switch SW1 is turned on, the switch SW1 can sink thepreset current I_(SRC) and discharge the control terminal G_(C). In onesuch embodiment, the control circuit 212 can alternately turn on and offthe switch SW1 thereby adjusting the battery current I_(CHG) to have atarget average level.

In the second mode in an embodiment, the voltage source 228 provides asecond reference voltage V_(CCR), and the amplifier 214B generates acompensation current I_(COM), according to a difference between thesense signal V_(SEN) and the reference signal V_(CCR), to charge ordischarge the compensation capacitor 230 to control a regulation signalS_(CCR). The regulation signal S_(CCR) can also be controlled by turningon the discharge switch 234. The regulation signal S_(CCR) includes avoltage on the capacitor 230 that controls a gate-source voltage of theswitch SW2. For example, if the sense signal V_(SEN) is greater than thereference signal V_(CCR), then the amplifier 214B outputs a currentI_(COM) to charge the compensation capacitor 230 to increase theregulation signal S_(CCR). If the sense signal V_(SEN) is less than thereference signal V_(CCR), then the amplifier 214B draws in a currentI_(COM) to discharge the compensation capacitor 230 to reduce theregulation signal S_(CCR). If the sense signal V_(SEN) is equal to thereference signal V_(CCR), then the amplifier 214B neither charges nordischarges the compensation capacitor 230 to maintain the regulationsignal S_(CCR). If the discharge switch 234 is turned on, thecompensation capacitor 230 can be discharged to pull down the regulationsignal S_(CCR). In an embodiment, the switch SW2 can pass a sink currentI_(SINK), e.g., from the current source 206 to a low-voltage terminal(e.g., reference ground), to sink at least a portion of the presetcurrent I_(SRC) under control of the regulation signal S_(CCR). Forexample, the sink current I_(SINK) increases if the regulation signalS_(CCR) increases, decreases if the regulation signal S_(CCR) decreases,or remains unchanged if the regulation signal S_(CCR) remains unchanged.Additionally, the control current I_(CTL) can charge the controlterminal G_(C) to increase the battery current I_(CHG) if the sinkcurrent I_(SINK) is less than the preset current I_(SRC), or dischargethe control terminal G_(C) to reduce the battery current I_(CHG) if thesink current I_(SINK) is greater than the preset current I_(SRC). In onesuch embodiment, the control circuit 212 can increase or decrease theregulation signal S_(CCR) thereby adjusting the battery current I_(CHG)to have a target current level.

In the example of FIG. 2B, the battery management module 200′ includesswitches SW1 and SW2, the comparator 214A, and the amplifier 214B, andtherefore the battery management module 200′ is compatible with morebattery packs having different current sense resistors. However, theinvention is not so limited. In another embodiment, the batterymanagement module can include the switch SW1 and the comparator 214A anddoes not include the switch SW2 and the amplifier 214B. In yet anotherembodiment, the battery management module can include the switch SW2 andthe amplifier 214B, and does not include the switch SW1 and thecomparator 214A.

FIG. 3A illustrates an example of a signal waveform for the batterycurrent I_(CHG) in an abovementioned first mode, in an embodiment of thepresent invention. FIG. 3A is described in combination with FIG. 2A andFIG. 2B. In the example of FIG. 3A, during the first time intervalT_(ON1), the battery current I_(CHG) is in a range determined by thereference signal V_(COC), e.g., the battery current I_(CHG) is less thana first reference current level I_(COC) given by:I_(COC)=V_(COC)/R_(SEN). Thus, the switch SW1 is turned off, and thecontrol current I_(CTL) charges the control terminal G_(C) of thecontrol switch 220 to increase the battery current I_(CHG). When thebattery current I_(CHG) increases to be out of the range, e.g., thebattery current I_(CHG) is equal to or greater than the current levelI_(COC), the comparison result S_(COC) controls the control circuit 212to turn on the switch SW1. Hence, the control current I_(CTL) dischargesthe control terminal G_(C) to turn off the control switch 220. Duringthe second time interval T_(OFF1), the battery current I_(CHG) decreasesto, e.g., zero amperes. Thus, the average level I_(AVE) of the batterycurrent I_(CHG) can be given by: I_(AVE)=0.5I_(COC)×T_(ON1)/T_(CYC1),where T_(CYC1) represents a cycle period of the battery current I_(CHG),e.g., a sum of the time intervals T_(ON1) and T_(OFF1).

In an embodiment, the control circuit 212 adjusts the ratioT_(ON1)/T_(CYC1) thereby adjusting the average level I_(AVE). Forexample, the control circuit 212 can increase the ratio T_(ON1)/T_(CYC1)(e.g., reduce the cycle period T_(CYC1)) thereby increasing the averagecurrent I_(AVE) if the battery voltage V_(BATT) increases or if adifference between the battery voltage V_(BATT) and the input voltageV_(PACK+) decreases. In another embodiment, the control circuit 212adjusts the reference voltage V_(COC) thereby adjusting the averagelevel I_(AVE). For example, the control circuit 212 can increase thereference voltage V_(COC) to increase the average level I_(AVE) if thebattery voltage V_(BATT) increases. As a result, the time for thepre-charge process in embodiments of the present invention can be lessthan that in the conventional pre-charge process described in relationto FIG. 1.

In an embodiment, the sense resistance R_(SEN) may be relatively small,e.g., smaller than specified resistance. Advantageously, in theabovementioned first mode, the battery management module 200′ can adjustthe battery current I_(CHG) relatively accurately even if the resistanceR_(SEN) is relatively small. It is because the comparison result S_(COC)is generated by comparing the peak voltage level of the sense signalV_(SEN) (e.g., indicative of the peak current level of the batterycurrent I_(CHG)) with the reference voltage V_(COC), and the peakvoltage level can be high enough to control the comparator 214Arelatively accurately even if the resistance of the sense resistorR_(SEN) is relatively small.

FIG. 3B illustrates an example of a signal waveform for the batterycurrent I_(CHG) in an abovementioned second mode, in an embodiment ofthe present invention. FIG. 3B is described in combination with FIG. 2Aand FIG. 2B. In the example of FIG. 3B, during a first time intervalT_(ON2), the battery current I_(CHG) is in a range determined by thereference signal V_(CCR), e.g., the battery current I_(CHG) is less thana second reference current level I_(CCR) given by:I_(CCR)=V_(CCR)/R_(SEN). Thus, the switch SW2 is turned off, and thecontrol current I_(CTL) charges the control terminal G_(C) of thecontrol switch 220 to increase the battery current I^(CHG). When thebattery current I_(CHG) increases to be out of the range, e.g., thebattery current I_(CHG) is equal to or greater than the current levelI_(CCR), the control current I_(CTL) can terminate the charging of thecontrol terminal G_(C). In an embodiment, when the battery currentI_(CHG) increases to the current level I_(CCR), the battery managementmodule can enter a steady state, e.g., during a third time intervalT_(CC) shown in FIG. 3B. In the steady state, the sense signal V_(SEN)substantially remains at the reference voltage level V_(CCR), e.g., thebattery current I_(CHG) substantially remains at the current levelI_(CCR). By way of example, if the sense signal V_(SEN) is greater thanthe reference voltage V_(CCR), e.g., the battery current I_(CHG) isgreater than the current level I_(CCR), then the regulation signalS_(CCR) increases the sink current I_(SINK) to be greater than thepreset current I_(SRC) thereby decreasing the sense signal V_(SEN). Ifthe sense signal V_(SEN) is less than the reference voltage V_(CCR),e.g., the battery current I_(CHG) is less than the current levelI_(CCR), then the regulation signal S_(CCR) decreases the sink currentI_(SINK) to be less than the preset current I_(SRC) thereby increasingthe sense signal V_(SEN). Thus, in the steady state, the amplifier 214Bcan maintain the sink current at a level of the preset current I_(SRC)thereby maintaining the sense signal V_(SEN) at a level of the referencevoltage V_(CCR), e.g., maintaining the battery current I_(CHG) at thecurrent level I_(CCR). In an embodiment, during a second time intervalT_(OFF2), the control circuit 212 can disable the sink current I_(SINK)by turning on the discharge switch 234.

In the example of FIG. 3B, the average level I_(AVE) of the batterycurrent I_(CHG) can be adjusted by adjusting the first time intervalT_(ON2), the cycle period T_(CYC2) of the battery current I_(CHG),and/or the reference voltage V_(CCR). For examples, if the batteryvoltage V_(BATT) increases, the control circuit 212 can increase thefirst time interval T_(ON2), and/or reduce the cycle period T_(CYC2),and/or increase the reference voltage V_(CCR), thereby increasing theaverage level I_(AVE) of the battery current I_(CHG). As a result, thetime for the pre-charge process in embodiments of the present inventioncan be less than that in the conventional pre-charge process describedin relation to FIG. 1.

In an embodiment, the sense resistance R_(SEN) may not be relativelysmall, e.g., greater than specified resistance, and therefore the sensesignal V_(SEN) can be high enough to control the amplifier 214Bappropriately even if the battery current I_(CHG) is relatively small.In one such embodiment, the battery management module 200′ can operatein the abovementioned second mode, in which the battery managementmodule 200′ increases the battery current I_(CHG) during the first timeinterval T_(ON2), maintains the battery current I_(CHG) at the currentlevel I_(CCR) during the third time interval T_(ON2), and disables thebattery current I_(CHG) during the second time interval T_(OFF2). In anembodiment, the battery management module 200′ may control the averagelevel I_(AVE) of the battery current I_(CHG) more accurately in thesecond mode compared with in the first mode. In an embodiment, thereference current level I_(CCR) (e.g., I_(CCR)=V_(CCR)/R_(SEN)) for thesecond mode is less than the reference current level I_(COC) (e.g.,I_(COC)=V_(COC)/R_(SEN)) for the first mode.

As discussed above, the battery management module 200′ can selectivelyoperate in the first mode or the second mode according to the senseresistance R_(SEN). However, the invention is not so limited, and thebattery management module 200′ may operate in the first and second modesin parallel in another embodiment. By way of example, the comparator214A and the amplifier 214B are enabled to perform the comparing processin parallel, and the first reference signal V_(COC) is set to be greaterthan the second reference signal V_(CCR). In an embodiment, if thebattery current I_(CHG) changes smoothly, then the battery currentI_(CHG) can be adjusted by the combined circuit of the amplifier 214Band capacitor 230. In another embodiment, if the battery current I_(CHG)changes quickly, e.g., a transient current, an impulse current, or thelike is presented in the battery current I_(CHG), then the combinedcircuit of the amplifier 214B and capacitor 230 may not be able toadjust the battery current I_(CHG) properly due its low-response speed.In one such embodiment, the battery current I_(CHG) can be adjusted bythe comparator 214A. For example, if the battery current I_(CHG)increases so quickly that the amplifier 214B is unable to maintain thebattery current I_(CHG) at the abovementioned second reference currentlevel I_(CCR) (e.g., determined by the second reference signal V_(CCR)),the comparator 214A can reduce the battery current I_(CHG) when thebattery current I_(CHG) increases to the abovementioned first referencecurrent level I_(COC). As a result, the battery current I_(CHG) can beadjusted appropriately.

As mentioned above, in embodiments of the present invention, the batterymanagement module 200′ can adjust the average level I_(AVE) of thebattery current I_(CHG) by adjusting the adjustable parameters such asthe time intervals T_(OH1), T_(CYC1), T_(ON2), T_(CC), and/or T_(CYC2),and/or the reference voltages V_(COC) and/or V_(CCR). Additionally, inembodiments of the present invention, the adjustable parameters can beadjusted based on performance parameters of the control switch 220(e.g., a charge switch or a discharge switch) such as maximum junctiontemperature, junction-to-ambient factor, and maximum pulse powerdissipation at room temperature. After setting the maximum allowedtemperature increase for the control switch 220, the maximum allowedaverage power dissipation can be estimated based on the performanceparameters. In an embodiment, the first time interval T_(ON1) orT_(ON2), or the duty cycle of the control switch 220, or the referencevoltage V_(COC) or V_(CCR) can be set to be as large as possible as longas the average power dissipation of the control switch 220 is less thanthe abovementioned maximum allowed average power dissipation.

FIG. 4 illustrates a topology of an example of a battery managementmodule 400, in an embodiment of the present invention. FIG. 4 isdescribed in combination with FIG. 2A, FIG. 2B, FIG. 3A and FIG. 3B. Inthe example of FIG. 4, the battery management module 400 controls adischarge switch 420 to control discharging of the battery 202, and thecontrolling of the discharge switch 420 is similar to the controlling ofthe charge switch 220 described in relation to FIG. 2A, FIG. 2B, FIG. 3Aand FIG. 3B. In other words, the BMU 404, current source 406, controlcircuit 412, comparator 414A, amplifier 414B, current regulator 416,charge pump 418, compensation capacitor 430, discharge switch 434, thirdswitch SW3, and fourth SW4 in FIG. 4 have functions similar to those ofthe abovementioned BMU 204, current source 206, control circuit 212,comparator 214A, amplifier 214B, current regulator 216, charge pump 218,compensation capacitor 230, discharge switch 234, first switch SW1, andsecond SW2, respectively.

In an embodiment, the discharge switch 420 passes a discharging currentI_(DSG) from the battery 202 to power a load (not shown) coupled to theterminals PACK+ and PACK−. The current regulator 416 cooperates with thecurrent source 418 to enable the discharging current I_(DSG) to flowthrough the battery 202 in a first time interval T_(ON), disable/cutoffthe discharging current I_(DSG) in a second time interval T_(OFF), andalternately enable and disable the discharging current I_(DSG). In anembodiment, the control circuit 412 controls a ratio of the first timeinterval T_(ON) to a sum T_(CYC) of the first and second time intervals(e.g., T_(CYC)=T_(ON)+T_(OFF)) according to a status of the load. Inanother embodiment, the control circuit 412 controls the referencevoltages V_(DOC) and/or V′_(CCR) according to the status of the load.

By way of example, the battery management module 400 can detect a statusof a load coupled to the terminals PACK+ and PACK− by generating apre-discharge current I_(DSG) (e.g., a discharge current at a relativelylow level) to the terminals PACK+ and PACK−. The battery managementmodule 400 can generate the pre-discharge current I_(DSG) in a mannersimilar to the generating of the pre-charge current I_(CHG) discussedabove, and control the pre-discharge current I_(DSG) to be relativelysmall, e.g., by controlling the parameters T_(ON), T_(ON)/T_(CYC),V_(DOC), and/or V′_(CCR) to be relatively small. In an embodiment, whenthe pre-discharge current I_(DSG) flows to the terminal PACK+, if thevoltage between the terminals PACK+ and PACK− is in a predeterminedvoltage range, then the battery management module 400 determines thatthere is a load coupled to the terminals PACK+ and PACK. If the voltageis below than the voltage range, then the battery management module 400may determine that the terminals PACK+ and PACK− are short-circuited. Ifthe voltage is above the voltage range, then the battery managementmodule 400 may determine that there is no load coupled to the terminalsPACK+ and PACK−. In an embodiment, if the load consumes less (or larger)power, then the battery management module 400 can reduce (or increase)the pre-discharge current I_(DSG) (e.g., by reducing (or increasing) theparameters T_(ON), T_(ON)/T_(CYC), V_(DOC), and/or V_(CCR)).

FIG. 5 illustrates a topology of an example of a battery system thatincludes multiple battery packs, in an embodiment of the presentinvention. FIG. 5 is described in combination with FIG. 2A, FIG. 2B,FIG. 3A, FIG. 3B, and FIG. 4. In the example of FIG. 5, only two batterypacks 500A and 500B are shown. However, the invention is not so limited,and in other embodiments of the present invention, the system caninclude arbitrary number of battery packs. In an embodiment, the BMUs504A and 504B can include circuits and functions similar to that of theBMU 204 and/or include circuits and functions similar to that of the BMU404. The BMU 504A can measure a battery voltage of the battery 502A anda battery system voltage (e.g., the input voltage) from terminal PACK+of the battery pack 500A. The BMU 504B can measure a battery voltage ofthe battery 502B and a battery system voltage (e.g., the input voltage)from terminal PACK+ of the battery pack 500B.

In an embodiment, the battery packs 500A and 500B are coupled inparallel, and their batteries 502A and 502B may have different voltagelevels. When the battery packs 500A and 500B are charged by a powersource 532 (e.g., a charger) or when the battery packs 500A and 500Bdischarge to power a load, if their charge switches Q_(CHGA) andQ_(CHGB) and discharge switches Q_(DSGA) and Q_(DSGB) are fully turnedon, then a large current may flow between the battery packs 500A and500B and it may destroy the circuits in the battery packs 500A and 500B.Advantageously, the BMU 504A and/or the BMU 504B can partially turn onthe switches to generate a pre-charge current I_(CHG) or a pre-dischargecurrent I_(DSG), and control the current I_(CHG) or I_(DSG) to berelatively small. As a result, the battery packs 500A and 500B can beprotected.

In an embodiment, assume that the power source 532 is not connected, anda new battery pack (e.g., the battery pack 500B) is plugged in thebattery system which includes battery 500A or more battery packs. If abattery voltage of the battery 502A is greater than a battery voltage ofthe battery 502B, then the battery pack 500B can be set in a pre-chargemode to increase its battery voltage until the battery voltage of thebattery 502B is substantially equal with the battery voltage of thebattery 502A. The pre-charge current is regulated and controlled by theBMU 504B. If a battery voltage of the battery 502A is less than abattery voltage of the battery 502B, the battery pack 500B can be set ina pre-discharge mode to decrease its battery voltage until the batteryvoltage of the battery 502B is substantially equal with the batteryvoltage of the battery 502A. The pre-discharge current is regulated andcontrolled by the BMU 504B.

In another embodiment, assume that the power source 532 is connected,and a new battery pack (e.g., the battery pack 500B) is connected to thebattery system which includes battery 500A or more battery packs, thevoltage of the power source 532 is higher than the battery voltage ofthe battery 502A and battery 502B. In this case, both the battery pack500A and the battery pack 500B are set in a charge mode. If the batteryvoltage of the battery 502A is greater than a battery voltage of thebattery 502B, the BMU 504A regulate the charge current of the battery502A, and the BMU 504B regulate the charge current of the battery 502A,such that the charge current of the battery 502A is less than the chargecurrent of the battery 502B. Consequently, the battery 502B is chargedfaster to achieve balance between the battery packs.

Additionally, in yet another embodiment, in a charging process in whichthe power source 532 provides power to the terminals PACK+ and PACK−, ifthe voltage of the battery 502A is greater than the voltage of thebattery 502B, then the BMU 504B fully turns on the charge switchQ_(CHGB), and the BMU 504A partially turns on the discharge switchQ_(DSGA) to generate a pre-discharge current. The pre-discharge current,together with the current from the power source 532, can flow to chargethe battery 502B, so as to balance the batteries 502A and 502B. By wayof another example, in a discharging process in which the battery packs500A and 500B provide power to a load, if the voltage of the battery502A is greater than the voltage of the battery 502B, then the BMU 504Afully turns on the discharge switch Q_(DSGA), and the BMU 504B partiallyturns on the charge switch Q_(CHGB) to allow a pre-charge current fromthe battery 502A to charge the battery 502B, so as to balance thebatteries 502A and 502B. In yet other examples, when the battery packs500A and 500B are neither charged by a power source nor discharging topower a load, if the voltage of the battery 502A is greater than thevoltage of the battery 502B, then the BMU 504A can partially turn on thedischarge switch Q_(DSGA) to generate a pre-discharge current, and theBMU 504B can fully turn on the charge switch Q_(CHGB) to allow thebattery 502B to be charged by the pre-discharge current from the battery502A; or the BMU 504A can fully turn on the charge switch Q_(CHGA) andthe discharge switch Q_(DSGA) and the BMU 504B can partially turn on thecharge switch Q_(CHGB) to allow a pre-charge current from the battery502A to charge the battery 502B. As a result, the batteries 502A and502B can be balanced with each other.

FIG. 6 illustrates a flowchart of examples of operations performed by abattery management module, e.g., 200, 200′, 400, or 500, in anembodiment of the present invention. FIG. 6 is described in combinationwith FIG. 2A, FIG. 2B, FIG. 3A, FIG. 3B, FIG. 4, and FIG. 5.

In block 602, the comparison circuitry 214 compares the sense signalV_(SEN), indicative of a battery current (e.g., a charging currentI_(CHG) or a discharging current I_(DSG)) flowing through the battery202 and a control switch (e.g., 220 or 410), with a reference signal(e.g., V_(COC), V_(CCR), V_(DOC), or V′_(CCR)) to generate a comparisonresult (e.g., S_(COC), S_(CCR), S_(DOC), or S′_(CCR)).

In block 604, the current generating circuitry 238 generates a controlcurrent I_(CTL) to charge or discharge a control terminal (e.g., gateterminal G_(C) or G_(D)) of the control switch thereby adjusting thebattery current to have a target average level.

In block 606, the current source (e.g., 206 or 406) generates a presetcurrent to charge the control terminal.

In block 608, the current regulator (e.g., 216 or 416) sinks at least aport of the preset current to regulate the control current according tothe comparison result.

FIG. 7 illustrates a topology of an example of a battery managementmodule 700, in an embodiment of the present invention. Elements labeledthe same in FIG. 2A have similar functions. The battery managementmodule 700 can be integrated in a battery pack.

In an embodiment, the battery management module 700 includes a battery202, a control switch 220 (e.g., a charge switch in the examples ofFIGS. 7 and 8 or a discharge switch in the example of FIG. 9), a currentsense element (e.g., including a resistor R_(SEN)) and a batterymanagement unit (BMU) 704. The BMU 704 includes voltage sense circuitry,a storage unit 702, a control circuit 712 and a current regulationcircuitry. In the example of FIG. 7, the control switch 220, e.g., acharge switch, can pass a battery current I_(CHG), e.g., a pre-chargingcurrent, from the input terminal PACK+ to the battery 202 if an inputvoltage at the input terminal PACK+ is greater than the battery voltageV_(BATT) of the battery 202. The current sense element provides a sensesignal V_(SEN) indicative of the battery current I_(CHG). The voltagesense circuitry includes a battery-voltage sense circuit 208 for sensingthe battery voltage V_(BATT) at an electrode (e.g., the anode) of thebattery 202 and an input-voltage sense circuit 210 for sensing an inputvoltage V_(PACK) at a power terminal (e.g., PACK+) of the battery pack.The storage unit 702 can store attribute data associated with thebattery pack. The attribute data can include parameters of the controlswitch 220 such as drain-to-source on-state resistance (Rdson), maximumallowed DC power, maximum pulse power, package type and thermalresistance. The attribute data can also include parameters of theprinted circuit board (PCB) implementing the BMU 704 such as the PCBlayout property and thermal performance. The storage unit 702 can beimplemented inside the battery pack or outside of the battery pack. Ifthe storage unit 702 is outside of the battery pack, the data stored init can be accessed by the control circuit 712 through a communicationinterface. The control circuit 712, coupled to the voltage sensecircuitry and the storage unit 702, is operable for adjusting a level ofa reference signal 722 based on the attribute data stored in the storageunit 702 and a difference between the battery voltage V_(BATT) and theinput voltage V_(PACK) sensed by the voltage sense circuitry. The levelof the reference signal 722 can determine a target level of the batterycurrent I_(CHG). The current regulation circuitry is operable forcontrolling the control switch 220 to regulate the battery currentI_(CHG) flowing through the control switch 220 and the battery 202according to the reference signal. In the example of FIG. 7, the currentregulation circuitry includes a comparison circuitry 714 and currentgenerating circuitry 738.

The comparison circuitry 714 can compare the sense signal V_(SEN) withthe reference signal 722 to generate a comparison result. The currentgenerating circuitry 738 can generate a control current I_(CTL),according to the comparison result, to charge or discharge a controlterminal G_(C) of the control switch 220 thereby adjusting the batterycurrent I_(CHG) to have a target average level. The control switch 220includes a field-effect transistor, e.g., a metal-oxide semiconductorfield-effect transistor, and the control terminal G_(C) includes a gateterminal of the field-effect transistor. The control current I_(CTL) cancharge the gate terminal G_(C) to increase the gate voltage V_(G) of thecontrol switch 220 to partially turn on the switch 220, therebyincreasing the battery current I_(CHG). The control current I_(CTL) canalso discharge the gate terminal G_(C) to reduce the gate voltage V_(G)thereby to reduce or cutoff the battery current I_(CHG). Thus, thebattery current I_(CHG) can be adjusted by adjusting the control currentI_(CTL). The abovementioned comparison result can be provided to thecurrent generating circuitry 738 to adjust the control current I_(CTL)such that the battery current I_(CHG) is adjusted accordingly.

In an embodiment, the current generating circuitry 738 includes acurrent source 206, a charge pump 218, and a current regulator 716. Thecurrent source 206 can generate a preset current I_(SRC) to charge thecontrol terminal G_(C). The charge pump 218 can provide a supply voltageto power the current source 206. The control circuit 712 can connect thecontrol terminal G_(C) to the supply voltage provided by the charge pump218 to fully turn on the control switch 220, or connect the controlterminal G_(C) to the current source 206 to partially turn on thecontrol switch 220. If the control switch 220 is partially turned on(e.g., operated in a linear mode), the current regulator 716 can sink atleast a portion of the preset current I_(SRC) to regulate the controlcurrent I_(CTL) according to the comparison result from the comparisoncircuitry 714. In an embodiment, if the battery current I_(CHG)decreases below a threshold, the control circuit 712 fully turns on thecontrol switch 220.

FIG. 8 illustrates circuit diagrams of examples of the current regulator716 and the comparison circuitry 714, in an embodiment of the presentinvention. Elements labeled the same in FIG. 2B have similar functions.As shown in FIG. 8, the current regulator 716 includes a switch SW2(e.g., including a metal-oxide-semiconductor field-effect transistor), acompensation capacitor 230, and a discharge switch 234. The comparisoncircuitry 714 includes an amplifier 214B and reference voltage source228. The voltage source 228 provides a reference signal V_(CCR) undercontrol of the control circuit 712, and the amplifier 214B generates acompensation current I_(COM), according to a difference between thesense signal V_(SEN) and the reference signal V_(CCR), to charge ordischarge the compensation capacitor 230 to control a regulation signalS_(CCR). The regulation signal S_(CCR) can also be controlled by turningon the discharge switch 234. The regulation signal S_(CCR) includes avoltage on the capacitor 230 that controls a gate-source voltage of theswitch SW2.

The control circuit 712, the current regulator 716 and the comparisoncircuitry 714 regulate the battery current I_(CHG) in a similar way asthe second mode of the battery management module 200′ of FIG. 2B. Byadjusting a level of the reference signal V_(CCR) according to theattribute data and the difference between the battery voltage V_(BATT)and the input voltage V_(PACK), the control circuit 712 can regulate abattery current to avoid large current surge. In an embodiment, thecontrol circuit 712 adjusts the reference signal V_(CCR) to maximize thebattery current within a safe range which is determined by the attributedata, so as to shorten the balancing time while preventing the circuitryfrom being damaged. Furthermore, the control circuit 712 can increasethe reference signal V_(CCR) if the difference between the batteryvoltage V_(BATT) and the input voltage V_(PACK) decreases.

Similar to the embodiment described in FIG. 3B, besides of adjusting thereference signal V_(CCR), the battery management module 800 can furtheradjust the time interval T_(ON2) during which the control switch 200 ison and/or duty cycle of the control switch 220 to adjust an averagelevel of the battery current I_(CHG).

FIG. 9 illustrates a topology of an example of a battery managementmodule 900, in an embodiment of the present invention. Elements labeledthe same in FIGS. 4 and 8 have similar functions. In the example of FIG.9, the battery management module 900 controls a discharge switch 420 tocontrol discharging of the battery 202. The discharge switch 420 canpass a battery current I_(DSG), e.g., a pre-discharging current, fromthe battery 202 to the terminal PACK+ if an input voltage at theterminal PACK+ is less than the battery voltage V_(BATT) of the battery202. The controlling of the discharge switch 420 is similar to thecontrolling of the charge switch 220 described in FIG. 8. The BMU 904,current source 406, control circuit 912, amplifier 414B, currentregulator 916, charge pump 418, compensation capacitor 430, dischargeswitch 434, and switch SW4 in FIG. 9 have functions similar to those ofthe abovementioned BMU 704, current source 206, control circuit 712,amplifier 214B, current regulator 716, charge pump 218, compensationcapacitor 230, discharge switch 234 and switch SW2, respectively.

It can be understood that, besides of the examples in FIGS. 7-9, otherapproaches can be utilized to control the control switch 220. Forexample, in an embodiment, a battery management module can include acomparison circuitry (e.g., amplifier) that compares a sensing signalindicative of the battery current and a reference signal indicative of atarget level of the battery current to output a comparison result (e.g.,a voltage signal). A level of the voltage signal varies with thedifference between the sensing signal and the reference signal. Thecontrol switch is controlled in a linear mode according to the voltagesignal. As a result, the battery current flowing through the controlswitch is regulated accordingly.

In the examples in FIG. 7-9, the control switches are implemented byN-channel metal-oxide semiconductor field-effect transistor (NMOSFET)coupled between anode of the battery 202 and the positive terminal PACK+of the battery pack. In other embodiments, control switches can beimplemented by NMOSFET coupled between cathode of the battery 202 andthe negative terminal PACK− of the battery pack.

FIG. 10 illustrates a topology of expandable battery system 1000 thatincludes multiple battery packs, in an embodiment of the presentinvention. FIG. 10 is described in combination with FIGS. 7-9. In theexample of FIG. 10, only two battery packs 1001A and 1001B are shown.However, the invention is not so limited, and in other embodiments ofthe present invention, the system can include arbitrary number ofbattery packs. In an embodiment, the BMUs 1004A and 1004B can includecircuits and functions similar to that of the BMU 704 and/or includecircuits and functions similar to that of the BMU 904.

The expandable battery system 1000 can be an energy storage system(ESS), an uninterruptible power supply (UPS) or a power tool, etc. In aconventional expandable battery system, bi-directional DC/DC convertersmay be used to avoid large current surge among battery packs caused byvoltage difference between battery packs during hot-swap plug-in.However, using bi-directional DC/DC converters not only increases costbut also reduces reliability. In contrast, the expandable battery system1000 according to present invention provides a low-cost and reliablesolution to regulate the current between battery and to avoid the largecurrent surge.

Assume that initially the battery pack 1001A is in operation and itscharge switch Q_(CHGA) and discharge switch Q_(DSGA) are fully turnedon. In order to expand the total capacity of the battery system 1000,the battery pack 1001B is planned to be assembled (plugged in) with thebattery pack 1001A. The charge switch Q_(CHGB) and discharge switchQ_(DSGB) of the battery pack 1001B are turned off first. After beingconnected with the battery pack 1001A, the battery pack 1001B senses aninput voltage V_(PACK) at the terminal PACK+ and a battery voltageV_(BATT2) of the battery 1002B. The input voltage V_(PACK) is determinedby the battery voltage of the battery 1002A in the battery pack 1001A.

If the battery voltage V_(BATT2) is less than the input voltageV_(PACK), the BMU 1004B partially turn on the charge switch Q_(CHGB) andcontrols the charge switch Q_(CHGB) in a linear mode. More specifically,a control circuit in the BMU 1004B adjusts a level of a reference signalbased on a difference between the battery voltage V_(BATT2) and theinput voltage V_(PACK) and based on attribute data associated with thebattery pack 1001B. The attribute data is pre-stored in a storage unit.The level of the reference signal can determine a target level of thebattery current which flows from the terminal PACK+ through the chargeswitch Q_(CHGB) to the battery 1002B. Accordingly, the battery 1002B ischarged by a regulated current. The control circuit controls the chargeswitch Q_(CHGB) to regulate the battery current according to thereference signal. As a result, large current surge between battery pack1001A and battery pack 1001B can be avoided, and battery pack 1001A andbattery pack 1001B can be balanced. In an embodiment, the controlcircuit increases the reference signal if the difference between thebattery voltage V_(BATT2) and the input voltage V_(PACK) decreases. Ifthe battery current, which is sensed by a current sense element in theBMU 1004B, decreases below a threshold, it indicates that two batterypacks have been balanced. In such situation, the BMU 1004B can fullyturn on the charge switch Q_(CHGB) and the discharge switch Q_(DSGB) ofthe battery pack 1001B to enable normal operation of the battery pack1001B.

If the battery voltage V_(BATT2) is greater than the input voltageV_(PACK), the BMU 1004B partially turn on the discharge switch Q_(DSGB)and controls the discharge switch Q_(DSGB) in a linear mode. Morespecifically, a control circuit in the BMU 1004B adjusts a level of areference signal based on a difference between the battery voltageV_(BATT2) and the input voltage V_(PACK) and based on attribute dataassociated with the battery pack 1001B. The attribute data is pre-storedin a storage unit. The level of the reference signal can determine atarget level of the battery current which flows from the battery 1002Bthrough the discharge switch Q_(DSGB) to the terminal PACK+.Accordingly, the battery 1002B is discharged by a regulated current. Thecontrol circuit controls the discharge switch Q_(DSGB) to regulate thebattery current according to the reference signal. As a result, largecurrent surge between battery pack 1001A and battery pack 1001B can beavoided, and battery pack 1001A and battery pack 1001B can be balanced.In an embodiment, the control circuit increases the reference signal ifthe difference between the battery voltage V_(BATT2) and the inputvoltage V_(PACK) decreases. If the battery current, which is sensed by acurrent sense element in the BMU 1004B, decreases below a threshold, itindicates that two battery packs have been balanced. In such situation,the BMU 1004B can fully turn on the charge switch Q_(CHGB) and thedischarge switch Q_(DSGB) of the battery pack 1001B to enable normaloperation of the battery pack 1001B.

In an embodiment, the expandable battery system 1000 further includes ahost controller 1134 and a system power source (e.g., a charger) 1032.The system power source 1032 can provide power to the system 1000 and aload 1038. The battery packs 1001A and 1001B, the load 1038 and the hostcontroller 1034 are all coupled to a communication line, (e.g., a bus)1136. The host controller 1034 can receive data from the battery packsand send command to control the battery pack via the communication line1136. For example, the host controller 1034 can send commands to abattery pack to adjust a charge current or a discharge current, or toenable or disable a battery pack to charge or discharge. Advantageously,charge current and discharge current of each battery pack can becontrolled according to attribute data associated with each batterypack, the power status of the power source 1032, status of each batterypack and status of the load to achieve safe and efficient operation ofthe system 1000.

FIG. 11 illustrates a flowchart of examples of operations performed by abattery management module, e.g., 700, 800, 900, in an embodiment of thepresent invention. FIG. 11 is described in combination with FIGS. 7-9.

In block 1102, voltage sense circuitry senses a battery voltage V_(BATT)of a battery 202 in the battery pack.

In block 1104, voltage sense circuitry senses an input voltage V_(PACK)of the battery pack.

In block 1106, a control circuit (e.g., 712 or 912) adjusts a level of areference signal based on attribute data associated with a battery packand a difference between the battery voltage V_(BATT) and the inputvoltage V_(PACK). In another embodiment, if a battery system (e.g., theexpandable battery system 1000) includes a host controller (e.g., 1134),the host controller can over-write the decision from each battery pack.In other words, in such embodiment, a level of a reference signal isadjusted by the host controller, rather than the control circuit insidea battery pack. The level of the reference signal can be adjusted by thehost controller based on attribute data associated with the batterypack, status of a system power source, status of a load and status ofthe battery pack. The host controller can transmit commands to eachbattery pack through a communication line (e.g., a bus) to adjust thereference signal. The host controller can also transmit command to eachbattery pack to turn on or turn off a control switch (e.g., a chargeswitch and/or a discharge switch).

In block 1108, current regulation circuitry controls the control switchto regulate the battery current which flows through the control switchand the battery according to the reference signal.

While the foregoing description and drawings represent embodiments ofthe present invention, it will be understood that various additions,modifications and substitutions may be made therein without departingfrom the spirit and scope of the principles of the present invention asdefined in the accompanying claims. One skilled in the art willappreciate that the invention may be used with many modifications ofform, structure, arrangement, proportions, materials, elements, andcomponents and otherwise, used in the practice of the invention, whichare particularly adapted to specific environments and operativerequirements without departing from the principles of the presentinvention. The presently disclosed embodiments are therefore to beconsidered in all respects as illustrative and not restrictive, thescope of the invention being indicated by the appended claims and theirlegal equivalents, and not limited to the foregoing description.

I claim:
 1. A battery system comprising a plurality of battery packs,wherein a battery pack of said battery packs comprises: a battery;voltage sense circuitry that senses a battery voltage of said batteryand an input voltage of said battery pack; a control circuit, coupled tosaid voltage sense circuitry, operable for adjusting a level of areference signal based on attribute data associated with said batterypack and a difference between said battery voltage and said inputvoltage; a control switch operable for passing a battery current flowingthrough said battery; and current regulation circuitry, coupled to saidcontrol circuit and said control switch, operable for controlling saidcontrol switch to regulate said battery current according to saidreference signal.
 2. The battery system of claim 1, wherein said controlcircuit is further operable for controlling said control switchaccording to command from a host controller.
 3. The battery system ofclaim 1, wherein said control circuit increases said reference signal ifsaid difference between said battery voltage and said input voltagedecreases.
 4. The battery system of claim 1, wherein said battery packfurther comprises: a current sense element that senses said batterycurrent, wherein said control circuit fully turns on said control switchif said battery current decreases below a threshold.
 5. The batterysystem of claim 1, wherein said current regulation circuitry comprises:comparison circuitry that compares a sense signal indicative of saidbattery current with said reference signal to generate a comparisonresult, wherein said control switch is controlled according to saidcomparison result.
 6. The battery system of claim 1, wherein saidcurrent regulation circuitry comprises: comparison circuitry thatcompares a sense signal indicative of said battery current with saidreference signal to generate a comparison result; and current generatingcircuitry, coupled to said comparison circuit, that generates a controlcurrent to charge or discharge a control terminal of said control switchthereby adjusting said battery current to have a target average level,wherein said current generating circuitry comprises: a current sourcethat generates a preset current to charge said control terminal; and acurrent regulator, coupled to said current source, that sinks at least aportion of said preset current to regulate said control currentaccording to said comparison result.
 7. The battery system of claim 6,wherein said current regulator comprises a first switch, coupled to saidcontrol terminal, that passes a sink current to sink at least a portionof said preset current under control of a regulation signal, and whereinsaid comparison circuitry comprises an amplifier that generates acompensation current, according to a difference between said sensesignal and said reference signal, to charge or discharge a compensationcapacitor, coupled to said first switch, to control said regulationsignal.
 8. The battery system of claim 7, wherein said amplifier reducessaid sink current if said sense signal is less than said referencesignal, increases said sink current if said sense signal is greater thansaid reference signal, and maintains said sink current at a level ofsaid preset current thereby maintaining said sense signal at a level ofsaid reference signal.
 9. A method comprising: sensing a battery voltageof a battery pack; sensing an input voltage of said battery pack;adjusting a level of a reference signal based on attribute dataassociated with said battery pack and a difference between said batteryvoltage and said input voltage; and controlling a control switch toregulate a battery current which flows through said control switch andsaid battery according to said reference signal.
 10. The method of claim9, further comprising: increasing said reference signal if saiddifference between said battery voltage and said input voltagedecreases.
 11. The method of claim 9, further comprising: sensing saidbattery current; and fully turning on said control switch if saidbattery current decreases below a threshold.
 12. The method of claim 9,further comprising: comparing a sense signal indicative of said batterycurrent with said reference signal to generate a comparison result; andcontrolling said control switch according to said comparison result. 13.The method of claim 9, further comprising: comparing a sense signalindicative of said battery current with said reference signal togenerate a comparison result; and generating a control current to chargeor discharge a control terminal of said control switch thereby adjustingsaid battery current to have a target average level, wherein saidgenerating said control current comprises: generating a preset currentto charge said control terminal; and sinking at least a port of saidpreset current to regulate said control current according to saidcomparison result.
 14. The method of claim 13, wherein said sinking atleast a port of said preset current to regulate said control currentaccording to said comparison result comprises: generating a regulationsignal to control a first switch, coupled to said control terminal, thatpasses a sink current to sink at least a portion of said preset currentto regulate said control current; and generating a compensation current,according to a difference between said sense signal and said referencesignal, to charge or discharge a compensation capacitor, coupled to saidfirst switch, to control said regulation signal.
 15. The method of claim14, further comprising: reducing said sink current if said sense signalis less than said reference signal; increasing said sink current if saidsense signal is greater than said reference signal; and maintaining saidsink current at a level of said preset current thereby maintaining saidsense signal at a level of said reference signal.
 16. A batterymanagement module comprising: comparison circuitry that compares a sensesignal, indicative of a battery current flowing through a battery and acontrol switch, with a reference signal to generate a comparison result;and current generating circuitry, coupled to said comparison circuit,that generates a control current to charge or discharge a controlterminal of said control switch thereby adjusting said battery currentto have a target average level, wherein said current generatingcircuitry comprises: a current source that generates a preset current tocharge said control terminal; and a current regulator, coupled to saidcurrent source, that sinks at least a portion of said preset current toregulate said control current according to said comparison result. 17.The battery management module of claim 16, wherein said control switchcomprises a field-effect transistor, and said control terminal comprisesa gate terminal of said field-effect transistor, and wherein saidcontrol current charges said gate terminal to increase a gate voltage ofsaid field-effect transistor thereby increasing said battery current.18. The battery management module of claim 16, wherein said currentregulator comprises a first switch, coupled to said control terminal,that sinks said preset current and discharges said control terminal whensaid first switch is turned on, and wherein said comparison circuitryturns on said first switch if said sense signal is greater than saidreference signal.
 19. The battery management module of claim 16, whereinsaid current regulator comprises a second switch, coupled to saidcontrol terminal, that passes a sink current to sink at least a portionof said preset current under control of a regulation signal, and whereinsaid comparison circuitry comprises an amplifier that generates acompensation current, according to a difference between said sensesignal and said reference signal, to charge or discharge a compensationcapacitor, coupled to said second switch, to control said regulationsignal.
 20. The battery management module of claim 19, wherein saidamplifier reduces said sink current if said sense signal is less thansaid reference signal, increases said sink current if said sense signalis greater than said reference signal, and maintains said sink currentat a level of said preset current thereby maintaining said sense signalat a level of said reference signal.
 21. The battery management moduleof claim 16, wherein said current generating circuitry enables saidbattery current to flow through said battery in a first time interval bycharging said control terminal, disables said battery current in asecond time interval by discharging said control terminal, andalternately enables and discharges said battery current.
 22. The batterymanagement module of claim 21, wherein said control switch comprises acharge switch that passes a charging current from a power source tocharge said battery, and wherein said battery management module furthercomprises a control circuit that increases a ratio of said first timeinterval to a sum of said first and second time intervals if a voltageof said battery increases.
 23. The battery management module of claim21, wherein said control switch comprises a discharge switch that passesa discharging current from said battery to power a load, and whereinsaid battery management module further comprises a control circuit thatcontrols a ratio of said first time interval to a sum of said first andsecond time intervals according to a status of said load.
 24. Thebattery management module of claim 16, wherein said control currentcharges said control terminal if said battery current is in a rangedetermined by said reference signal, and terminates charging of saidcontrol terminal if said battery current is outside of said range, andwherein said battery management module further comprises a controlcircuit that adjust said reference signal thereby adjusting said targetaverage level.
 25. The battery management module of claim 24, whereinsaid control circuit increases said reference signal to increase saidtarget average level if a voltage of said battery increases.